The use of Bacillus anthracis as a bioweapon depends on dispersal of its spores in the environment, entrance into the body, spore uptake by the human host cells, germination of the spores in the host, and the pathological consequences of the host response to the toxins elaborated by the vegetative cells within the host. Very little is known of the mechanisms of spore entry into the host, including targeted cell types at the surface of airways, digestive tract, and skin, and their subsequent initial encounter with cellular and humoral elements of the innate and adaptive immune response. An understanding of these host-spore interactions and the very early events that occur as the spores initiate the germination process will likely permit the development of an interventional vaccine or drug strategy that would act prior to the germination of spores and outgrowth of the vegetative form within the host and thus prevent development of Anthrax. We will identify mouse cell types and pathways involved in initial B. anthracis spore contact, and transport after binding to antigen processing cells following airway, intestinal or skin application. These goals will be achieved by a combination of flow cytometric analysis and analysis of tissue sections of skin, lung, and gut tissues. We will determine sites of residual spore retention and whether they induce chronic spore-specific immune responses that can be measured as an indicator of the spore load. If we can induce passive protective immunity with antibodies, we will attempt to elicit similar vaccine-induced immune responses and test the effects of these in long-term memory responses and determine the intracellular fate of spores if they are opsonized with different monoclonal antibodies. We will determine the basis for the sporicidal or germination inhibitory activity of antibodies. We will analyze such activity with classic bacteriological techniques as well as morphological studies. By identifying the spore-associated target molecules of these antibodies, we will be able to identify potential mechanisms to rapidly inactivate spores prior to establishment of infectious loci and vegetative cell outgrowth resulting in death from toxemia and septicemia. Therapeutic strategies of this nature would be a major supplement to the current PA-based vaccines as well as to the current recommended antibiotic regimens and in the case ofmultidrug-resistant B. anthracis strains engineered to produce additional toxins.